A new meta-study, which followed 267,000 people, sheds a few answers

For exercise enthusiasts and those who study the mind-body connection—or perhaps better put, the mind-body system—it has long been known that physical activity helps with depression. And yet even as evidence for this effect continues to mount, “the incorporation of exercise as a key component in the treatment of depression is inconsistent,” write Felipe Barreto Schuch and Brendon Stubbs in the most recent issue of Current Sports Medicine Reports. Schuch and Stubbs, researchers at the University of Santa Maria in Brazil and King’s College in London, respectively, go on to explain that exercise ought to be more seriously considered and prescribed in treatment protocols, in the same way that talk therapy and medication, the two most common responses to depression, are. To support this recommendation, Schuch and Stubbs recently undertook a comprehensive review of exercise and depression. Here is a summary of the results.

Can Exercise Prevent Depression?

Lotsofstudies show that the more someone exercises, the less likely they are to have depression. This is true across cultural contexts. The challenge with these studies is that they are associative only. Yes, people may not experience depression because they exercise. But it’s also quite possible that people don’t exercise because they are depressed.

In an attempt to tease out the causal effect of exercise—that is, whether or not exercising is actually protective against depression—Schuch and Stubbs only reviewed studies that were designed as prospective cohorts. This means that a group of people who had no signs of depression were followed for at least one year. Researchers could then look at whether or not the people who exercised more had a lower incidence of depression. For their review, Schuch and Stubbs included 49 such studies that, taken together, followed 267,000 people and included different types of exercise. They found that exercise reduced the chances someone would experience depression by between 17 and 41 percent—a substantial effect that was observed across different countries, ages, and sexes.

Put simply: exercise helps prevent depression. Just because you exercise doesn’t mean you won’t ever become depressed, but it certainly reduces the chances that you will.

Can Exercise Treat Already-Existing Depression?

“Exercise can improve depressive symptoms in people with depression,” write Schuch and Stubbs. “However, similar to other treatments, exercise is not a panacea and may not work equally for all.”

Every part of the above statement is important. Exercise can—and often does—help, but not always and not for everyone. I know many people who experience (or have experienced) depression and who get so fed up when they are told, “Just exercise more.” If it were that easy, everyone would do it.

That said, there is convincing evidence that exercise should absolutely be included in a broader tool kit to help people who are experiencing depression. Schuch and Stubbs conducted a review of 25 studies that surveyed a total of 1,487 people and found that between 40 and 50 percent of people with depression respond to exercise, with an effect that, on a scale of small, medium, or large, is considered large. This on par with talk therapy and medication. And while the dropout rate for exercise is around 18 percent, it is 19 percent for talk therapy and between 26 and 28 percent for medication. It’s also important to note that these treatments are not exclusive and can be used together to great benefit.

How Does Exercise Prevent and Treat Depression?

According to Schuch and Stubbs, the neurobiological mechanisms underpinning the antidepressant effects of exercise are still unclear. However, there are a few hypotheses. Depression is associated with chronic inflammation, and regular exercise reduces inflammation. Depression is also associated with lower levels of a chemical called BDNF, which helps the brain grow and remodel. Regular exercise increases BDNF, so it could help a depressed brain outgrow its patterns.

Exercise is also associated with positive psychological changes. It increases confidence and self-determination and often takes place in a community, all of which are helpful for depression. Though pharmaceutical companies would surely love to zero in on a singular pathway for exercise’s positive effects on depression (so they could make a drug to mimic it), they shouldn’t get their hopes up. Exercise’s benefit is probably in the combination of all these pathways, and likely others we aren’t even aware of yet.

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